A hybrid vehicle in which a first motor/generator, an oil pump, a first clutch, a belt type continuously variable transmission, a second clutch, and a second motor/generator are disposed between an engine and a driven wheel is known from Japanese Patent Application Laid-open No. 2001-200920. This conventional hybrid vehicle starts off and accelerates by means of the driving force of the engine, and the driving force of the engine is assisted by making the first motor/generator function as a motor; during cruising, the engine is stopped, and the vehicle travels by making the second motor/generator function as a motor; and during deceleration, electrical energy is recovered by making the first and second motor/generators function as generators.
When the engine is running, it is possible to generate a hydraulic pressure for shifting the belt type continuously variable transmission with the oil pump, which is driven by the engine, but when the engine is stopped and the vehicle travels by means of the driving force of the second motor/generator, since the oil pump generates no hydraulic pressure, when switching from traveling by means of the driving force of the second motor/generator to traveling by means of the driving force of the engine, there is a time lag until the oil pump generates a hydraulic pressure and shifting of the belt type continuously variable transmission becomes possible, and there is a possibility that the ratio control responsiveness might be degraded thus causing shift shock to occur.
In the above-mentioned conventional arrangement, in addition to the oil pump driven by the engine, an electric oil pump is provided, and by generating a hydraulic pressure with the electric hydraulic pump when the engine is stopped, the actual ratio of the belt type continuously variable transmission is rapidly made to coincide with a target ratio when switching over from traveling by means of the driving force of the second motor/generator to traveling by means of the driving force of the engine,.
However, in the above-mentioned conventional arrangement, since it is necessary to employ an electric oil pump in addition to the oil pump driven by the engine, there is the problem that the number of components, cost, space, weight, etc. are increased by an amount corresponding to the electric oil pump and a motor for driving it.